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In Reply to: RE: Futterman H3 amp 'upgrades' posted by rogerh113 on July 31, 2019 at 10:31:43
Or is it actually an H3a or aa? The difference between an H3 and H3a is that Futterman used one single very large electrolytic capacitor to couple the output to the speaker, in the H3. In the H3a, he went to using a gaggle of physically smaller photoflash capacitors, which were the fastest available in his day. Nowadays, I recommend subbing either type of output capacitor with a bunch of high quality Panasonics or Nichicons, to reach the sum total of whatever you've got now, and beyond. Then bypass the electrolytics with the best highest value film cap you can find, etc. The originals are probably shot, anyway.
Follow Ups:
It looks to be a Harvard Electronics H3, and has the large coupling caps. I am considering getting it as a project.
If the objective is to optimize the sound of the amp, is it also useful to replace the resistors? I am thinking that is probably the case.
That leads to an interesting problem. As it is, it is a time-capsule with regards to being a very good condition H3. But it is not useful as an amp.
If I really wanted to do some basic improvements to enhance the performance, a lot is changed and it is no longer really a H3, aside from the case, transformer, tube holders, and a few more parts. Easy to get carried away and remove the convenience outlate and put in an IEC and some modern speaker wire lugs - likely to improve functionality. Destroys the history of the amp, but makes it (hopefully) highly usable.
Likely anyone getting the amp will have to do some of this, but it seems a bit odd right now.
I don't suggest changing the circuit. That is a very tricky business, anyway. The only real "upgrades" I know about are the ones made by the engineer for NYAL. (I think his name is or was "Hammond".) Supposedly that improved bass response. Otherwise, if you are just upgrading or renewing parts, I would not think you devalue it for a collector. Hang on to the original parts; that should mollify any purist collector.
Ralph or Bruce Rozenblitt of Transcendent would know exactly how Hammond changed the circuit. I would change out any and all electrolytics, the outputs as noted, and the coupling capacitors because there are much better ones these days. Resistors generally hold up well, but if you have carbon resistors, they do change value with age and use and should be replaced where necessary. Unless you have a schematic, you will have to rely on reading the color coded bands on each resistor to determine their intended value.
Julius built two amplifiers for me in the late 1970s, when he was working with one assistant out of a small "factory" off Broadway on 72nd St, toward the end of his life. The second effort was an H3aa with the photoflash caps. He was a very kind, very humble man. He made his own power transformers in that loft. One day when I went up there, several freshly made ones were hanging up to dry and reeking of PCBs. Not exactly a "safe" workplace.
I would absolutely retain the circuit exactly as it is, and merely improve the components. I have heard that these amps can sound great, and I don't want to lose that. I also know I don't have the skills nor the interest in changing anything to do with the circuit.
Sounds like a great experience going the shop and interacting with Futterman. There is a lot of history to the Futterman, which is one of the really compelling things for me.
Until I switched to Atma-sphere and the circlotron in the mid-1990s, I owned one or another variant of the Futterman OTL from the early 1970s. They were great driving any ESL I could throw at them, including KLH9s, the first version of the M-L CLS (which was a high impedance speaker), and even one conventional speaker with ESL tweeters that I built myself.
Would you recommend the Futterman? I would be driving an Altec 604 (very efficient and 8 ohms).
yes.
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